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The Universe is expanding Right?

  1. Sep 8, 2004 #1
    I was just listening to 'The galaxy song' by monty python and I got thinking.

    The general belief (i think) is that its relatively early after the big bang and the universe is expanding, but what proof is there that we're not compressing? that we're already in the second stage of the universe and moving together?
     
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  3. Sep 8, 2004 #2

    russ_watters

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    Virtually all galaxies we see are red-shifted, for one. Cosmological Microwave Background radiation for another.
     
  4. Sep 8, 2004 #3

    Eh

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    Light from galaxies would be blue shifted in a contracting universe, I believe.
     
  5. Sep 8, 2004 #4
    whats red shifted and blue shifted mean then?
     
  6. Sep 9, 2004 #5

    Chronos

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  7. Sep 17, 2004 #6
    When an atom emits radiation, it does so at very specific wavelengths, such that each atom has its own set of characteristic wavelengths. It is a signature. Hydrogen has its signature wavelengths, helium, carbon etc. When we detect the hydrogen signature somewhere in space, we know there are hydrogen atoms there.

    The hydrogen signatures (spectra) from galaxies however, are all shifted towards longer wavelengths compared to the hydrogen spectra we measure on Earth or elsewhere in our own galaxy (sun hydrogen etc.).

    Now imagine listening to a car running by you. High pitch as it nears, lower pitch as it moves away. For lightwaves, a high pitch (high frequency) corresponds to a shift toward shorter frequencies (represented as "blue"), and the lower pitch corresponds a shift towards the "red" end of the EM spectrum.

    If all hydrogen spectra from galaxies are shifted to longer wavelengths (towards "red"), the natural conclusion is that like the car emitting lower pitched sound waves, they must be getting further.
     
    Last edited by a moderator: Sep 17, 2004
  8. Sep 21, 2004 #7
    The expanding universe

    You bring up a good question. Red shifts and blue shifts are called the Doppler effect. The Doppler effect is present in all forms of energy waves whether they are from a motorboat cruising through the water (kinetic water waves). Sound waves and light waves. The Doppler effect can be directly observed when a train is approaching with its whistle blowing. As the train approaches the sound waves are compressed at the front of the train and the whistle has a higher pitch. As the train moves away the pitch gets lower as the waves are elongated from the receding train engine. You can observe the phenomena visually when riding in a boat. If you look at the water in the front of the boat you will see the water waves as being compressed and then elongated on the sides of the boat.
    Red shifts and blue shifts are just markers scientist use in white light (the colors of the light spectrum). This helps cosmologist to tell in which direction objects in space are moving relative to us. Red shifted light is an object moving away from us and a blue shift means it is moving towards us.

    Although it is generally accepted in cosmology that the universe is expanding, Doppler red shifts only show objects are moving away from us. They do not PROVE the universe is expanding though it is widely accepted that the universe is indeed expanding. Doppler red shifts are also seen on the event horizon of black holes in which the universe is contracting regionally (if there is such a thing as “locality”)
     
  9. Sep 23, 2004 #8
    wavelength

    Is there any way to explain without using long equations,( or if using long equations please explain thoroughly), why the energy that is given from speed becomes part of the wavelength frequency energy?
     
  10. Sep 23, 2004 #9
    What if the universe isn't expanding?

    What if it is nothing more than a mere illusion created by extraterrestrial means? One of the reasons why were are not picking up hundreds and hundreds of radiowaves, from this galaxy and several nearby ones.
     
    Last edited: Sep 23, 2004
  11. Sep 23, 2004 #10

    Nereid

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    Welcome to Physics Forums Super_Saiyan!

    Indeed, in physics we do ask a lot of 'what if?' questions. Being a branch of science, however, we also check for consistency, especially with observational and experimental results. In this case, your statement is quite inconsistent with observations ... the whole of radio astronomy is about 'picking up radiowaves, from this galaxy and several nearby ones' ... and more distant ones, and (if you class microwaves as 'radiowaves') right back to the time of ~300,000 years after the Big Bang.
     
  12. Sep 24, 2004 #11
    As simple as I can put it :

    You can run into or away from a galaxy just like you can run into or away from a pitcher. The energy perceived from the photon or baseball depends on your own motion away or towards the source (galaxy or pitcher).
     
  13. Sep 26, 2004 #12

    Aki

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    What would happen if the universe is completly static, it neither expands nor contracts? How is that going to affect us?
     
  14. Sep 26, 2004 #13

    Chronos

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    This is how the big bang was sniffed out. Einstein realized the universe cannot be completely static. Without an opposing force, gravity would cause it to collapse. The big bang provided the initial momentum required to avoid immediate collapse and dark energy is the remnant force that is barely sufficient to keep it from collapsing.
     
  15. Sep 26, 2004 #14
    Does dark matter actually exist? Did the big bang really happen? I think Aki has a point. The universe CAN be static. Anything is possible. Is there really an end ot this universe?? If there is, what is it like after the end? How do you know where the end is; is there a sign that says, "The Universe Ends Here. Please, turn your space shuttle around. Thank You!"
     
  16. Sep 26, 2004 #15

    Tom Mattson

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    You can't just make any proposal you like under the banner, "Anything is possible". That isn't science. One has to look at experimental evidence to look for what is really happening. And the evidence says that gravity is an attractive force (surprise, surprise). Since all masses in the universe are attracted to all other masses, there cannot be static equilibrium.
     
  17. Sep 26, 2004 #16

    Nereid

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    I'm from Missouri, show me that 'anything is possible'! In other words, describe a static universe and show that, in your description, it is consistent with all good experimental and observational results.
     
  18. Sep 26, 2004 #17
    No no, there could be one, but it will be unstable equilibrium

    That's generally what scientists are hoping against.
    Although Hawking didn't use aliens, he put it as a universe behaving by the will of God. Now I don't know how many of you believe in God, but if there is some unexplainable force causing all particles to behave the way they do, then that's pretty much a universe with chaos.

    The three possibilities offered by Hawking, or rather 4 with this one are:

    a) a universe that can be explained by a GUT (Grand Unified Theory)
    b) a universe that can be explained by a series of unconnectable theories
    c) a universe with random order
    d) the will of God
     
  19. Sep 27, 2004 #18

    Nereid

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    Moving this to General Astronomy & Cosmology, seems more appropriate than Stellar Astrophysics.
     
  20. Sep 27, 2004 #19

    Nereid

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    Welcome to Physics Forums 123rock!

    This takes rather a long way from experimental cosmology, don't you think?

    As we are limited to making observations and doing experiments, what gives us the confidence that we could ever reach an 'ultimate answer' re the origin and evolution of the universe? At any time, someone could do an experiment or make an observation which would show a previously unknown (and unanticipated) aspect of the universe that is inconsistent with the best GUT/union of the set of unconnectable theories/random order/will of dog/whatever ... and we have no way of knowing, in advance of that experiment or observation, just what that inconsistency would be! :surprised :tongue: :bugeye: :biggrin:

    In any case, as has been discussed in many threads in the Philosophy of Science and Mathematics, your #4 doesn't help at all (e.g. not testable, not distinguishable from #3).
     
  21. Sep 27, 2004 #20

    Garth

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    Actually it depends on what 'ruler' you use to measure the size of the universe.

    For example:

    If that ruler depends on the size of an atom then the universe is expanding w.r.t. the length of the ruler.

    If the ruler depends on the wavelength of a photon, for example sampled from the frequency of peak intensity of the CMB black body spectrum, then the universe is static: photons "expand" with the universe.

    Just a thought - Garth
     
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